Growth of SrBi4Ti4O15 thin films in a microwave oven by the polymeric precursor method

SrBi4Ti4O15 (SBTi) thin films were obtained by the polymeric precursor method and crystallized in a domestic microwave oven. For comparison, films were also crystallized in a conventional furnace at 700 degrees C for 2 h. Structural and morphological characterization of the SBTi thin films was investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Using platinum coated silicon substrates configuration, ferroelectric properties of the films were determined with remanent\polarization P-r and a coercive field E-c of 5.1 mu C/cm(2) and 135 kV/cm for the film thermally treated in the microwave oven and 5.4 mu C/cm(2) and 85 kV/cm for the film thermally treated in conventional furnace, respectively. The films thermally treated in the conventional furnace exhibited excellent fatigue-free characteristics up to 10(10) switching cycles indicating that SBTi thin films can be a promise material for use in non-volatile memories. (C) 2007 Elsevier B.V. All rights reserved.

Effect of oxidizing atmosphere on the electrical properties of SrBi4Ti4O15 thin films obtained by the polymeric precursor method

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Dynamics of meso and thermo citrate synthases with implicit solvation

The dynamics of hydration of meso and thermo citrate synthases has been investigated using the EEF1 methodology implemented with the CHARNM program. The native enzymes are composed of two identical subunits, each divided into a small and large domain. The dynamics behavior of both enzymes at 30 degrees C and 60 degrees C has been compared. The results of simulations show that during the hydration process, each subunit follows a different pathway of hydration, in spite of the identical sequence. The hydrated structures were compared with the crystalline structure, and the root mean square deviation (RMSD) of each residue along the trajectory was calculated. The regions with larger and smaller mobility were identified. In particular, helices belonging to the small domain are more mobile than those of the large domain. In contrast, the residues that constitute the active site show a much lower displacement compared with the crystalline structure. Hydration free energy calculations point out that Thermoplasma acidophilum citrate synthase (TCS) is more stable than chicken citrate synthase (CCS), at high temperatures. Such result has been ascribed to the higher number of superficial charges in the thermophilic homologue, which stabilizes the enzyme, while the mesophilic homologue denatures. These results are in accord with the experimental found that TCS keeps activity at temperatures farther apart from the catalysis regular temperature than the CCS. (c) 2005 Wiley Periodicals, Inc.

DC Electric Field Dependence of the Dielectric Constant of Pzt Thin Films Prepared by Polymeric Precursor Method

This work reports dielectric measurements performed on Pb(Zr0.53Ti0.47)O3 (PZT) thin films prepared by a polymeric precursor method. The -E curves obtained for the PZT film measured at 100 kHz, under a small ac 0.2 kV/cm signal-test and a dc scan featured a typical butterfly curve. However, the -E curves obtained for PZT film under a dc scan, with a scan rate of 0.003 V/s, shows a pronounced asymmetry. The absence of a symmetric secondary peak in -E curves could be an indication of essentially 180 domain switching.

Anticaries effect of dentifrices with calcium citrate and sodium trimetaphosphate

Because of the growing concerns regarding fluoride ingestion by young children and dental fluorosis, it is necessary to develop new dentifrices. Objective: The aim of this study was to evaluate the effect of dentifrices with calcium citrate (Cacit) and sodium trimetaphosphate (TMP) on enamel demineralization. Material and Methods: Enamel blocks (n=70), previously selected through surface hardness analysis, were submitted to daily treatment with dentifrices diluted in artificial saliva and to a pH-cycling model. The fluoride concentration in dentifrices was 0, 250, 450, 550, 1,000 and 1,100 mu g F/g. Crest (TM) was used as a positive control (1,100 mu g F/g). Cacit (0.25%) and TMP (0.25%) were added to dentifrices with 450 and 1,000 mu g F/g. Surface hardness was measured again and integrated loss of subsurface hardness and fluoride concentration in enamel were calculated. Parametric and correlation tests were used to determine difference (p<0.05) and dose-response relationship between treatments. Results: The addition of Cacit and TMP did not provide a higher fluoride concentration in enamel, however it reduced (p<0.05) mineral loss when compared to other dentifrices; the dentifrice with Cacit and TMP and a low fluoride concentration presented similar results when compared to a dentifrice with 1,100 mu g F/g (p>0.05). Conclusions: Dentifrices with 450 and 1,000 mu g F/g, Cacit and TMP were as effective as a gold standard one.

Effects of neonatal clomiphene citrate on fertility and sexual behavior in male rats

In order to investigate the participation of estrogen during the period of brain sexual differentiation, male rats were treated with clomiphene citrate in the neonatal phase. Fertility and sexual behavior were assessed during adult life. Sexual maturation, body weight, and wet weight of the testes were unchanged. Although the adult male rats treated with clomiphene in the neonatal phase presented a significant reduction in the frequency of mounts, 90% of these rats were able to mate with normal females, which became pregnant. However, these females exhibited a significantly increased number of pre- and post-implantation losses. When these adult male rats were castrated and received estrogen, 60% presented female sexual behavior (receptive behavior and acceptance of mount). Thus, treatment of pups with clomiphene immediately after birth has a long-term effect on the reproductive physiology and sexual behavior of male rats. (C) 2002 Elsevier B.V. All rights reserved.

Characterization of silica-carbon mesoporous matrix with embedded nickel nanoparticles synthesized by the polymeric precursor method

Nickel nanoparticles into silica-carbon matrix composites were prepared by using the polymeric precursor method. The effects of the polyester type and the time of pyrolysis on the mesoporosity and nickel particle dispersion into non-aqueous amorphous silica-carbon matrix were investigated by thermogravimetric analysis, adsorption/desorption isotherms and TEM. A well-dispersed metallic phase could be only obtained by using ethylene glycol. Weightier polyesters affected the pyrolysis process due to a combination of more amounts of carbonaceous residues and delaying of pyrolysis process. The post-pyrolyzed composites were successfully cleaned at 200 degrees C for I h in oxygen atmosphere leading to an increase in the surface area and without the occurrence of carbon combustion or nickel nanoparticles oxidation. The matrix composites presented predominantly mesoporous with pore size well defined in 38 angstrom, mainly when tetraethylene glycol was used as polymerizing agent. (C) 2007 Elsevier B.V. All rights reserved.

Characterization of the columbite precursor and (1-x)PMN-xPT powders prepared by Ti-modified columbite route

This study proposes to synthesize (1-x)PMN-xPT powders, where 0.10 < x < 0.45, using the T-modified columbite route. This methodology consists in the preparation of the MNT columbite precursor via the polymeric precursor method, followed by the solid state reaction with PbO to get the PMN-PT powders. It was verified that from 15 mol% of Ti, the MNT presents the coexistence of two main phases with different crystal symmetry: Rutile and Columbite. However, the synthesis of (1-x)PMN-xPT powders is not affected by this event. A detailed study of structural effects in MNT and PMN-PT powders as function of Ti content was made using the Rietveld method. It was also demonstrated that powders possess high chemical and microstructural homogeneity.

Expression and processing of recombinant sarafotoxins precursor in Pichia pastoris

Sarafotoxins are peptides isolated from the Atractaspisw snake venom. with strong constrictor effect on cardiac and smooth muscle. They are structurally and functionally related to endothelins. The sarafotoxins precursor cDNA predicts an unusual structure 'rosary-type', with 12 successive similar stretches of sarafotoxin (SRTX) and spacer, in the present work, the recombinant precursor of SRTXs was sub-cloned and expressed in the yeast Pichia pastoris. and secreted to the culture medium, Characterization by SDS-PAGE, immunoblot, mass spectrometry and biological activity, suggests that intact precursor was expressed but processing into mature toxins also occurred. Furthermore, our results indicate that the correct proportion of sarafotoxin types as contained in the precursor, is obtained in the yeast culture medium. Contractile effects of the expressed toxins, on rat and Bothrops jararaca isolated aorta, were equivalent to 5 X 10(-10) M and 5 x 10(-11) M of sarafotoxin b, respectively. The enzymes responsible for the complete maturation of sarafotoxins precursor are still unknown. Our results strongly suggest that the yeast Pichia pastoris is able to perform such a maturation process. Thus, the yeast Pichia pastoris may offer an alternative to snake venom gland to tentatively identify the molecular process responsible for SRTXs release. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Efeito da adição de dopantes durante a síntese do precursor columbita para a preparação da cerâmica ferroelétrica relaxora PMN

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Microwave-assisted hydrothermal synthesis of structurally and morphologically controlled sodium niobates by using niobic acid as a precursor

There are many advantages to using a microwave as a source of heat in hydrothermal reactions. Because it is a quick and homogeneous way to crystallize ceramic powders, it was used in this work for the production of antiferroelectric sodium mobate (NaNbO3) in a cubic-like form and its intermediary phase, disodium diniobate hydrate (Na2Nb2O6 center dot H2O), with a fiber morphology. The syntheses were carried out by treating niobic acid (Nb2O5 center dot nH(2)O) with NaOH. By changing the reaction time and the concentration of the reactants, particles with different structures and different morphologies could be obtained. The structural evolution of the products of this reaction was elucidated on the basis of the arrangement of the NbO6 octahedral units. Conclusive results were obtained with morphological and structural characterizations through XRD, TEM, MEV, and NMR and Raman spectroscopy. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

Effect of citrate ions on the electrochemical behaviour of low-carbon steel in borate buffer solutions

The electrochemical behaviour of cold-rolled low carbon steel was studied on both active and passive potential regions in borate buffer solutions with and without the addition of sodium citrate (NaCit). In the active region anodic charges increased significantly and RCT values decreased with citrate, due to the formation of soluble complexes. In the passive potential region the film formed at +0.4 V in borate buffer solution with and without 0.010 M NaCit is probably enriched by Fe3O4 oxide, while films formed at +0.8 V are probably enriched by gamma-Fe2O3. The equivalent circuit [R-s(R(CT)Q)] fitted all experimental impedance data. (C) 2003 Elsevier Ltd. All rights reserved.

Potassium niobate thin films prepared through polymeric precursor method

Thin films of potassium niobate were deposited on (100) Si substrates by the polymeric precursor method (Pechini method). Annealing in static air was performed at 600degrees C for 20 h. The obtained films were characterized by X-ray diffraction and atomic force microscopy (AFM). Electrical characterization of the films pointed to ferroelectricity via hysteresis loop. The dielectric constant, dissipation factor and resistance were measured in frequency region from 10 Hz to 10 MHz. At 1 MHz, the dielectric constant was 158 and the dissipation factor was 0.11. (C) 2004 Elsevier B.V. All rights reserved.

Effect of precursor solution on the formation of perovskite phase of Pb(Mg-1/Nb-3(2/3))O-3 thin films

Precursor solutions for Pb(Mg1/3Nb2/3)O-3 (PMN) synthesis were obtained by Pechini's method. The influence of the concentration of organic materials on the phase formation has been studied. For this purpose, PMN solutions were prepared with different precursors and were characterized by thermogravimetric and differential thermal analysis. The obtained solutions were deposited onto a Si (100) substrate by dip coating and pre-treated in a hot plate at 300 degreesC for 1 h. The films were annealed at 600, 700, 800 and 900 degreesC for 1 h and characterized by X-ray diffraction. The perovskite phase was formed after annealing at 600 and 700 degreesC when the solution of PMN was prepared with a lower amount of organic material and starting with mobium oxide. By increasing the temperature to 800 or 900 degreesC, only the formation of pyrochlore phase was observed. With the solution prepared from mobium ethoxide, only the presence of pyrochlore phase was observed independently of the annealing temperature. (C) 2002 Elsevier B.V. B.V. All rights reserved.